Donald, So sorry for your loss and the passing of Mason. You have a good vet who was honest with you and provided the needed information for you to make the right decision. Be very thankful for that. I have lost many dogs over the years. It never ever gets any easier. That being said I am glad you still have another dog that provides you the compansionship you desire.
Good Luck on adjusting to his passing, and remember there are lots of shelter and rescue dogs that need good homes like yours.